Add query syntax support for upserts
SQLite: https://www.sqlite.org/lang_UPSERT.html

MySQL: https://dev.mysql.com/doc/refman/8.0/en/insert.html

MariaDB: https://mariadb.com/kb/en/library/insert-on-duplicate-key-update/

PostgreSQL: http://www.postgresqltutorial.com/postgresql-upsert/

Unit tests, example queries